Our long-term goal is to understand neuronal mechanisms that underlie hearing. All acoustic information from the environment enters the brain via the auditory nerve and synpases in the cochlear nucleus. The cochlear nucleus in turn gives rise to the ascending pathways. The perception of sound is normally attributed to processing by these ascending pathways, but data are accumulating that stimulus context also plays a major role. That is, the meaning of a sound depends not only on spectral and temporal characteristics, but also on the past history and behavioral state of the animal. This contextual information could be provided by descending auditory pathways and neural systems not traditionally considered "auditory." In this application, we plan to study the interface between these ascending and descending systems. We propose that the granule cell domain of the cochlear nucleus represents a key site for the integration of multimodal influences. Preliminary data reveal that, in addition to descending auditory projections, there are somatosensory, vestibular and motor inputs to the granular cell domain. For the present application, we will apply anterograde and retrograde tract tracing methods to identify these neurons and their circuits, immunocytochemical staining procedures to reveal the chemistry of the different neurons and their terminals, and electrophysiological recording techniques to characterize the response properties of neurons projecting to this region. The data from this research will provide new knowledge on the synpatic organization of the highly integrative structure in the auditory system, and yield insights into how diverse neural systems shape the coding process for hearing.